Study highlights increase in use of high-dose vitamin D supplements

Consumer use of dietary supplements delivering vitamin D doses up to 4,000 IU – almost seven times the current recommended daily amount of 600 IU – says a new study published in JAMA.

Data from 1999 through 2014 indicated that 3% of the population may be taking vitamin D supplements at doses of 4,000 IU or more, exceeding the daily upper limit considered to possibly pose a risk of adverse effects, report scientists from the University of Minnesota, Johns Hopkins University, and the NIH’s Office of Dietary Supplements.

“Characterizing trends in vitamin D supplementation, particularly at doses above the tolerable upper limit, has important and complex public health and clinical implications,” ​wrote the authors.

Study details​

Using data from 39,243 participants of the nationally representative National Health and Nutrition Examination Survey (NHANES), the researchers assessed daily supplemental vitamin D intake of 1,000 IU or more and 4,000 IU or more from 1999 through 2014.

The data indicated that the prevalence of daily supplemental vitamin D use of 1,000 IU or more in 2013-14 was 18.2%, up from 0.3% in 1999-2000. In addition, the prevalence of daily supplemental intake of 4,000 IU or more in 2013-14 was 3.2%, up from less than 0.1% prior to 2005-6.

25(OH)D levels were stable from 1988 to 2006, but an increase was observed from 2007-2010.

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).

Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.

While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.

Interest in the potential health benefits of the sunshine vitamin has increased significantly over the last decade or more (see Google Trends figure below), while the 2015 Dietary Guidelines Advisory Committee classed the vitamin as a nutrient of concern.​

Andrea Wong, PhD, vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, told us: “Vitamin D is a shortfall nutrient and so you may say that this [increase in the use of high-dose vitamin D supplements] is not a bad thing: There are those people who are deficient who would need vitamin D supplements at or above the UL to achieve adequacy, and this would need to be done in consultation with a healthcare practitioner. ​

“For others, if they are considering high-dose supplements then this should be done after testing with a healthcare practitioner.​ You need to consider this in the context of individual needs.”​